The subject matter disclosed herein relates to a method and system for performing a biopsy of an object guided by a 3D image of the object obtained from digital tomosynthesis. More particularly, the disclosure relates to a simplified method and system for performing a guided breast biopsy using digital breast tomosynthesis.
Mammography is the principal method of identifying a lump or lesion found within a breast. Once a lesion is located, a biopsy is typically performed to obtain a tissue or cell sample, which allows for determination as to whether the lesion is benign or malignant. The biopsy may be performed through surgery or by inserting a needle into an object, such as a breast, and removing a sample using a needle and/or aspiration. Locating the lesion prior to the biopsy can be difficult, and various methods have been developed to aid in lesion location. Known methods of locating the lesion prior to a biopsy result in missed targets due to insufficient geometric accuracy. At this time, two methods of locating a lesion predominate, the first of which uses ultrasound, and the second of which relies on multiple images. In the first method, ultrasound is used to guide the needle or vacuum-assisted biopsy device to the target location of the lesion. In the second method, at least two images of the lesion visible under x-rays are taken at two known angles, and the x, y, and z coordinates of a point from the lesion's positions in the two angulated views is computed. Because the object may change shape, these past attempts at locating the lesion could involve multiple attempts at inserting the needle or the vacuum assisted biopsy tool, causing pain and discomfort to the patient.
Presently, devices have been developed to assist in positioning a tool using tomosynthesis. Digital Tomosynthesis provides a 3D image of a scanned object by taking x-ray images. For example, a breast may be compressed in a stationary position and x-ray images taken at multiple angles during a Digital Breast Tomosynthesis “DBT” scan. From this set of images a reconstruction is performed which generates an image or projections of the complete volume under the form of a large number of images representing cross-sections (“slices”) of the object computed at small intervals, e.g. 1 mm or less. The slices can be examined to identify and locate the lesion within the breast. DBT imaging provides better visibility creating improved contrast and visibility.
Once a lesion is identified, current methods of determining an entry point for a biopsy tool involve identifying the coordinates of the target, including the depth the tool is to be inserted. Once the coordinates are determined, the coordinates are transferred to a stage. This stage is moved into place automatically if motorized or manually, and will direct the needle into the breast. The stage uses 3D coordinates of the target identified through analysis of the DBT images or stereotactic pair to move the biopsy device and needle to the proposed coordinates of the target. In known techniques, the needle location is verified before the breast biopsy is performed. Verification of the needle is accomplished by inserting the needle into the breast about two centimeters from the center of the target, due to the distance between the tip of the needle and the side window through which the biopsy is performed, and performing additional image scans or x-rays to verify the needle location relative to the target. After the needle location is verified by confirming it was inserted 2 cm from the target, the needle is then moved to the proposed location of the target, and the needle is inserted into the breast to reach the target. Once the needle is inserted into the location believed to correspond to the target, another scan or image is acquired to verify the needle has reached the lesion prior to any tissue being sampled.
A problem of the method discussed above is that it requires an explicit computation of the x-y-z coordinates of the target point and the transfer of these coordinates to the stage. An additional problem of the method discussed above is the size and weight of the stage, whether the stage is motorized or manual. The reliance on the stage, which positions the biopsy tool, can be complicated and can require a motor as well as a position display at a significant cost. The stage is also bulky and takes up valuable space in a facility where biopsy procedures may be performed.
Two dimension approaches have also been developed; however, a problem with the “2D-localization” approaches occurs when the image of an indicator disposed on the paddle forms a conic projection when superimposed on the lesion. In the current 2D approach, when the needle is pushed perpendicular to the paddle or detector, a systematic error results. Except for structures on the line perpendicular to the detector and intersecting the focal spot, the angulation of the beam will generate an error in the location of the paddle projecting on the same point of the detector as the target. This error can oftentimes cause the target to be missed. This problem is worsened if the needle is inserted at a significant angle.